Conventionally, to the end of preventing the forgery of, for instance, a magnetic card, it has been practiced to use a laminated structure for its magnetic layer, and to punch holes in the magnetic card when the magnetic card is not intended for repeated use. However, such structures can be duplicated with deceitful intention by the forgers with relative ease, and may not be sufficient to discourage attempts to illegally duplicate and alter the card. The internal structure of the card may be made more complex by known means, but it will lead to the complication and cost increase of the reader/writers for reading and writing information into and out of the card.